1. Field of the Invention
The subject invention is directed to fuel nozzles for gas turbine engines, and more particularly, to an air swirler for fuel nozzles having aerodynamically shaped helical turning vanes for efficiently turning the air flow passing through the swirler while minimizing the risk of separation.
2. Description of Related Art
In a fuel nozzle for a gas turbine engine, compressor discharge air is used to atomize liquid fuel. More particularly, the air provides a mechanism to breakup a fuel sheet into a finely dispersed spray that is introduced into the combustion chamber of an engine. Quite often the air is directed through a duct that serves to turn or impart swirl to the air. This swirling air flow acts to stabilize the combustion reaction.
There are many ways to develop swirl in a fuel nozzle. Historically, helical vanes were used because of their ability to effectively turn the air flow. These vanes generated acceptable air flow characteristics for many engine applications. However, when a higher swirl factor was desired for certain engine application, there was a tendency for the air flow to separate from the helical vanes. This was generally associated with a reduction in the effectiveness of the geometric flow area of the nozzle.
To mitigate separation, vanes were designed with multiple joined leads that could aid in turning the air flow. These vanes were typically associated with a higher effectiveness of the geometric flow area of the nozzle. Such improvements resulted in a more effective use of the air velocity for atomization.
Air swirlers have also been developed that employ aerodynamic turning vanes, as described in U.S. Pat. No. 6,460,344 to Steinthorsson et al., the disclosure of which is incorporated herein by reference in its entirety. These airfoil shaped turning vanes are effective to impart swirl to the atomizing air flow. However, they provide a substantially uniform velocity profile at the nozzle.
It would be beneficial to provide an air swirler for a fuel nozzle having turning vanes that incorporate the beneficial aspects of multiple joined helical leads and an aerodynamic shape. In so doing, air flow through the swirler could be efficiently turned while the risk of separation would be minimized.